Method for impregnation of molecular sieve-binder extrudates

ABSTRACT

Method for impregnating a Group VIII metal on a molecular sieve-binder extrudate wherein the binder comprises a low acidity refractory oxide binder material, which is essentially free of alumina, by 
     a) contacting the molecular sieve-binder extrudate with an aqueous solution of a corresponding Group VIII metal nitrate salt having a pH of below 8, wherein the molar ratio between the Group VIII metal cations in the solution and the number of sorption sites present in the extrudate is equal to or larger than 1, and 
     b) drying the molecular sieve-binder extrudate obtained from step a).

FIELD OF THE INVENTION

The invention relates to a method for impregnating a Group VIII metal ona molecular sieve binder extrudate.

BACKGROUND OF THE INVENTION

PCT patent publication No. WO-A-9641849 describes an impregnation ofplatinum or palladium on a dealuminated silica-bound ZSM-5 with anaqueous solution of tetramine platinum hydroxide or tetramine palladiumhydroxide. The impregnation of the silica-bound ZSM-5 was followed bydrying for 2 hours at 120° C. and calcined for 2 hours at 300° C.Thereafter the catalyst was activated by reduction of the platinum orpalladium.

A disadvantage of the impregnation method described in PCT patentpublication No. WO-A-9641849 is the long drying time. The use of shorterdrying times results in a less favourable distribution of the platinumor palladium on the silica-bound ZSM-5. It is generally known that abetter distribution is possible when the molecular sieve is transformedbefore impregnation from its H-form to a NH₄-form. By an “NH₄-form” isunderstood that (part of) the H+ ions in the molecular sieve areexchanged for ammonium-ions.

An example of the transformation of a molecular sieve in a NH₄-formbefore impregnation is described in US patent publication U.S. Pat. No.5,397,454. This patent publication describes the impregnation of SSZ-32zeolite powder with palladium. Before impregnation the zeolite wassubjected to a sequence of 4 NH₄NO₃-ion exchanges. Hereafter it wasslurried into an aqueous solution of NH₄OH. Then a tetramine palladiumnitrate solution, of which the pH was adjusted to 9.5 with NH₄OH, wasadded slowly.

A disadvantage of this method is the long processing time forimpregnation. It would be advantageous if the extrudate with themolecular sieve in its H-form could be used directly in the process ofimpregnating a molecular sieve-binder extrudate.

The object of the present invention is to provide a method forimpregnating a Group VIII metal on a molecular sieve-binder extrudate,which allows a short drying time and results in a good distribution.Short drying times are desirable when a catalyst is prepared on acommercial scale.

SUMMARY OF THE INVENTION

This object has been achieved when the following steps are used forimpregnating a Group VIII metal on a molecular sieve-binder extrudatewherein the binder comprises a low acidity refractory oxide bindermaterial, which is essentially free of alumina. In particular it relatesto a method for impregnating a Group VIII metal on such a molecularsieve-binder extrudate by ion exchange with an aqueous solution of aGroup VIII metal salt. Such steps comprise:

a) contacting the molecular sieve-binder extrudate with an aqueoussolution of a corresponding Group VIII metal nitrate salt having a pH ofbelow 8, wherein the molar ratio between the Group VIII metal cations inthe solution and the number of sorption sites present in the extrudateis equal to or larger than 1, and

b) drying the molecular sieve-binder extrudate obtained from step a).

DETAILED DESCRIPTION OF THE INVENTION

It has been found that with the process according to the invention agood group VIII metal distribution is obtained, while short drying timesare possible. A further advantage is that the molecular sieve ormolecular sieve-binder extrudate can be directly used in its H-formwithout the need to first transform the molecular sieve in a NH₄-form.

The choice of molecular sieve is not essential for obtaining theadvantages of the invention, namely good distribution and short dryingtimes. Examples of molecular sieves include metallosilicates,metallophosphates and silica metallophosphates. Possible metallocomponents in the framework of these molecular sieves include metalssuch as Al, Fe, B, Ga or Ti or combinations of these metals. Preferredmolecular sieves are aluminosilicates, alumino phosphates and silicaaluminium phosphates, such as SAPO-11, SAPO-31 and SAPO-41. Especiallypreferred molecular sieves are aluminosilicates, further referred to aszeolites. Examples of suitable zeolites include ZSM-4 (Omega), ZSM-5,ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, Beta, X,Y and Las well as ferrierite and mordenite and isotypic framework structuresthereof. When the catalyst, resulting after impregnation of themolecular sieve-binder extrudate, is to be used for catalytic dewaxingpurposes, the preferred zeolite crystallites suitably have pores with amaximum diameter in the range of from 0.35 to 0.80 nm. Preferred zeolitecrystallites include MFI-type zeolites having pores with diameters of0.55 and 0.56 nm, such as ZSM-5 and silicalite, offretite having poreswith diameters of approximately 0.68 nm and zeolites of the ferrieritegroup having pores with diameter of 0.54 nm, such as ZSM-35 andferrierite. Another preferred class of zeolite crystallites includeTON-type zeolites. Examples of TON-type zeolite crystallites are ZSM-22,Theta-1 and Nu-10 as described in U.S. Pat. No. 5,336,478, EP-A-57049and EP-A-65400. A further preferred class of zeolite crystallites are ofthe MTW-type. Examples of molecular sieve crystallites having theMTW-type topology are ZSM-12, Nu-13, TEA-silicate, TPZ-3, TPZ-12, VS-12and Theta-3 as for example described in U.S. Pat. No. 3,832,449,EP-A-513118, EP-A-59059 and EP-A-162719. A next preferred class ofzeolite crystallites are of the MTT-type. Examples of zeolitecrystallites having the MTT-type topology are ZSM-23, SSZ-32, ISI-4,KZ-1, EU-1, EU-4 and EU-13 as for example described U.S. Pat. Nos.4,076,842, 4,619,820, EP-A-522196, EP-A-108486 and EP-A-42226.

The primary crystallite size of the molecular sieve can vary within awide range of 0.001 mm to 5 mm. For catalytic dewaxing purposes thecrystallite size of the zeolite may suitably be as high as 100 micron.Preferably small crystallites are used in order to achieve an optimumcatalytic activity. Preferably crystallites smaller than 10 micron andmore preferably smaller than 1 micron are used.

The binder of the molecular sieve-binder extrudate comprises a lowacidity refractory oxide binder material, which is essentially free ofalumina. Suitable binder materials, then, include low acidity refractoryoxides such as silica, zirconia, titanium dioxide, germanium dioxide,boria and mixtures of two or more of these. The most preferred binder,however, is silica. The binder may occur naturally or may be in the formof gelatinous precipitates, sols or gels. The binder may also be presentas a mixture of those. Preferred extrudates are those prepared by themethod described in U.S. Pat. No. 5,053,374.

The weight ratio of the molecular sieve and the binder can be anywherebetween 5:95 and 95:5. Lower molecular sieve content may in some casesbe advantageous for achieving a higher selectivity and higher molecularsieve content is to be preferred when a higher activity is desired.

After extrusion the molecular sieve-binder extrudate is dried for a timein the range of 15 minutes to 24 hours, more preferably from 1 to 3hours, at a temperature in the range from 10 to 350° C., more preferablyfrom 120 to 150° C. Thereafter the catalyst composition is subjected tocalcining under normal conditions, suitably at a temperature of between400 to 900° C. by heating in air for 1 to 48, preferably 1 to 10 hours.

Step a) of the method of the invention comprises contacting themolecular sieve-binder extrudate with an aqueous solution of acorresponding Group VIII metal nitrate salt having a pH of below 8,wherein the molar ratio between the Group VIII metal cations in thesolution and the number of sorption sites present in the extrudate isequal to or larger than 1. Preferably the molar ratio between the GroupVIII metal cations and the number of sorption sites is between 1 and 20.A sorption site is a site where theoretically one Group VIII cation canbe adsorbed. Calculation of the number of sorption sites per gramextrudate can be done as follows. An extrudate has a fixed value ofmoles H+ per gram extrudate. The number of moles H+ per gram extrudateis determined by means of NH₃-temperature programmed desorption (TPD) asis described in Zeolites, 19:288-396, 1997. The molar number of sorptionsites according to the present invention is the number of moles H+ pergram extrudate divided by the valency of the cation to be impregnated.The molar ratio between the Group VIII metal cations and the number ofsorption sites is thus defined as the number of moles of the Group VIIImetal cation divided by the molar number of sorption sites as definedabove. It is to be understood that after impregnation, the resultingcatalyst (containing the modified molecular sieve-binder extrudate) may,and normally will, contain more Group VIII metals than the amount ofwhich would be expected when the number of sorption sites is taken intoaccount. Preferably the final catalyst has a molar ratio of Group VIIImetal cations present in the extrudate and the number of sorption sitespresent in the extrudate equal to the ratio defined above.

The above mentioned ratio can be achieved in every way known in the art.For example such a ratio can be achieved by using a high amount or ahigh concentration of Group VIII metal nitrate salt in an aqueoussolution to such an extent that the above mentioned ratio is obtained.

In a preferred embodiment the above mentioned ratio is obtained byreducing the number of sorption sites in the molecular sieve ormolecular sieve-binder extrudate before contacting the molecularsieve-binder extrudate with the solution in step a). The number ofsorption sites in the molecular sieve or molecular sieve-binderextrudate can be reduced by reducing the number of acid sites of themolecular sieve crystallites. A reduction of the number of acid sitescan be achieved by methods known in the art, for example by subjectingthe molecular sieve-binder extrudate to a hydrothermal treatment, forexample by steaming the particles at a temperature of between 400 and900° C.

If the molecular sieve-binder extrudate contains aluminosilicates as amolecular sieve, it has been found advantageous to subject the molecularsieve or molecular sieve-binder extrudate to a dealumination treatmentprior to impregnation with the group VIII metal according to the methodof the invention. Dealumination results in a reduction of the number ofalumina moieties present in the aluminosilicate and hence in a reductionof the mole percentage of acid sites and hence in the number of sorptionsites. Dealumination can be attained by methods known in the art.Particularly useful methods are those, wherein the dealuminationselectively occurs, or anyhow is claimed to occur selectively, at thesurface of the crystallites of the molecular sieve.

Examples of dealumination processes are described in WO-A-9641849.Preferably dealumination is performed by a process in which themolecular sieve or the molecular sieve-binder extrudate is contactedwith an aqueous solution of a fluorosilicate salt wherein thefluorosilicate salt is represented by the formula:

(A)_(2/b)SiF₆

wherein ‘A’ is a metallic or non-metallic cation other than H+ havingthe valence ‘b’. Examples of cations ‘b’ are alkylammonium, NH₄ ⁺, Mg⁺⁺,Li⁺, Na⁺, K⁺, Ba⁺⁺, Cd⁺⁺, Cu⁺, Ca⁺⁺, Cs⁺, Fe⁺⁺, Co⁺⁺, Pb⁺⁺, Mn⁺⁺, Rb⁺,Ag⁺, Sr⁺⁺, Tl⁺, and Zn⁺⁺. Preferably ‘A’ is the ammonium cation. Themolecular sieve or molecular sieve-binder extrudate material may becontacted with the fluorosilicate salt in an amount of at least 0.0075moles per 100 grams of the molecular sieve or molecular sieve-binderextrudate material. The pH is suitably between 3 and 7. An example ofthe above described dealumination process is described in U.S. Pat. No.5,157,191.

The method according to the invention can suitably be used forimpregnation of any Group VIII metal, for example Pt, Pd, Ni, Ru and Co.The corresponding Group VIII metal nitrate salt can be a simple salt,such as for example Ni(NO₃)₂, or a complex salt, such as for examplePt(NH₃)₄(NO₃)₂, Pd(NH₃)₄(NO₃)₂, Pt(NH₃)₆(NO₃)₄ or Pd(NH₃)₆(NO₃)₄. Forcatalytic dewaxing purposes, salts of Pt, Pd, Ni, and mixtures thereofare preferred, and Pt is especially preferred. Preferred Group VIIImetal nitrate salts for catalytic dewaxing are Ni(NO₃)₂, Pt(NH₃)₄(NO₃)₂and Pd(NH₃)₄(NO₃)₂.

The total amount platinum, palladium or nickel, impregnated on themolecular sieve-binder extrudate, is suitably lower than 10% by weightcalculated as element and based on total weight of molecularsieve-binder extrudate, and preferably is in the range of from 0.01 to5.0% by weight, more preferably from 0.1 to 1.0% by weight.

For the impregnation of the molecular sieve-binder extrudate accordingto the method of the invention, use can be made of the varioustechniques known in the art, such as for example circulating solutionimpregnation and pore volume impregnation. Preferably pore volumeimpregnation is used, which is a very time-efficient technique. In thistechnique the volume of the solution containing the Group VIII metalsalt, which is contacted with the extrudate, is about equal to the porevolume of the molecular sieve-binder extrudate to be impregnated (seealso Studies in Surface Science and Catalysis, vol. 58, Introduction tozeolite science and practice, H. van Bekkum et.al. Elsevier, 1991, page503).

The concentration of the aqueous solution of Group VIII metal salt usedto achieve the required amount of metal distributed on the molecularsieve-binder extrudate can vary within wide ranges and effects theduration of the impregnation. The preferred concentration of Group VIIImetal salt is less than 20%. When using pore volume impregnation, theconcentration is preferably within the range of 0.02 to 10.0% by weight,most preferably from 0.2 to 2.0%. The molecular sieve-binder extrudateis contacted with the solution for a time effective to impregnate theGroup VIII metal salt. The duration of the impregnation suitably variesfrom 5 minutes to 24 hours, more preferably varies from 5 minutes to 3hours.

The aqueous solution used in step (a) has a pH of less than 8,preferably between 3.5 and 7. The aqueous solution may contain ammoniumions provided the pH is within the claimed range. Preferablyammonium-ions are essentially absent from the solution.

The temperature applied in step (a) is not critical and can vary withina range of below room temperature up to about 100° C., more preferablywithin a range of 15 to 65° C. Preferably the impregnation is performedat room temperature for reasons of convenience.

The pressure may vary within wide ranges and is not critical. Forreasons of convenience the impregnation according to step (a) of themethod of the invention is preferably conducted under atmosphericpressures.

Other metals may optionally be present in the molecular sieve ormolecular sieve-silica extrudate, before impregnation with the GroupVIII metal nitrate salt according to the method of the invention.

Step b) according to the method of the invention comprises drying themolecular sieve-binder extrudate obtained from step a). The in step a)modified molecular sieve-binder extrudate can suitably be dried attemperatures ranging from room temperature to 350° C., according to anydrying profile known in the art. In a preferred embodiment the molecularsieve-binder extrudate is dried according to an accelerated dryingprofile having a duration of less than 90 minutes, in which thetemperature is increased from about room temperature up to more than200° C., preferably up to more than 250° C. The drying profile cancomprise a continuous, linear or non-linear, increase of thetemperature, or can comprise stages in which the temperature is raisedand stages in which the temperature is maintained stable. For batch-wiseprocesses a preferred accelerated drying profile comprises the followingsteps: raising the temperature at a rate in the range of 10° C. to 20°C. per minute, to a temperature in the range of 150° C. to 200° C.;maintaining this temperature for an amount of time in the range of 5 to15 minutes; raising the temperature at a rate in the range of 10° C. to40° C. per minute, to a temperature in the range of 250° C. to 300° C.;maintaining this temperature for an amount of time in the range of 10 to20 minutes; cooling down to room temperature. For continuous processes apreferred accelerated drying profile comprises a continuous temperatureincrease, wherein the increase can be gradually or wherein the rate oftemperature increase varies. The use of this accelerated drying profilecan decrease the drying time which is especially advantageous when acatalyst is prepared on a commercial scale. As will become clear fromthe examples, impregnation according to the method of the inventionallows one to use such an accelerated drying profile while stillobtaining a good distribution of the metal over the molecularsieve-binder extrudate.

After drying, the molecular sieve-binder extrudate is optionallycalcined at a temperature between about 350° C. and 500° C.

The catalyst containing the molecular sieve-binder extrudate may beactivated before use, in any way known in the art, for example byreducing of the Group VIII cation with hydrogen.

The catalyst resulting after the treatment of a molecular sieve-binderextrudate according to the method of the invention can be used in anyhydrocarbon conversion reaction. Examples of such hydrocarbon conversionreactions are hydrocracking, isomerization, alkylation, hydrogenation,dehydrogenation, polymerization, reforming, catalytic cracking andcatalytic hydrocracking. The catalyst may be suitably used in catalyticdewaxing. By catalytic dewaxing is meant a process for decreasing thepour point of lubricating base oil products by selectively convertingthe components of the oil feed which impart a high pour point toproducts which do not impart a high pour point. Products which impart ahigh pour point are compounds having a high melting point. Thesecompounds are referred to as waxes. Wax compounds include for examplehigh temperature melting normal paraffins, iso-paraffins and mono-ringedcompounds. The pour point is preferably reduced by at least 10° C. andmore preferably by at least 20° C. Examples of such catalytic dewaxingprocesses are described in the before mentioned PCT patent publicationNo. 9641849.

The catalyst can be used in the catalytic dewaxing of any kind ofhydrocarbon feed. Suitably the catalyst can be used in the catalyticdewaxing of lubricants, base oil products, gas oils and feeds havingrelatively high amounts of waxy compounds. Examples of feeds with a highamount of waxy compounds are synthetic waxy raffinates (Fischer-Tropschwaxy raffinates), hydrocracker bottom fractions (hydrowax) and slackwaxes obtained from the dewaxing of hydroprocessed or solvent refinedwaxy distillates.

The method of the invention will now be illustrated by the followingnon-limiting examples.

Comparative example A

ZSM-5/silica extrudate (30%/70% w/w, calcined at 800° C.) was treatedwith a 0.01 M aqueous ammonium hexafluorosilicate (AHS) solution,washed, dried and calcined. The extrudate contained 0.048 H+ mmoles/gramextrudate. Hereafter 22.65 gram of the extrudate was impregnated withabout 0.7% w/w platinum by pore volume impregnation in 5 minutes with16.23 ml of a 5.0 M aqueous solution containing 2.79 gram of a tetramineplatinum hydroxide (Pt(NH₃)₄(OH)₂)-solution (5.9% w/w Pt). The pH of thesolution was >8. The impregnated extrudate was not washed, but driedaccording to a slow drying profile by; drying during 2 hours at 120° C.;whereafter the temperature was raised with 25° C./minute to 190° C. andheld stable during 1 hours; whereafter the temperature was raised againwith 50° C./minute to a temperature of 300° C. and held stable during 1hour. Hereafter the extrudate was cooled down to room temperature. The0.048 H+ mmoles/gram extrudate correspond with 0.024 mmoles sorptionsites for Pt 2+ cations. 22.65 gram extrudate contains 0.54 mmolessorption sites. From the above it can be calculated that the solutioncontained 0.84 mmoles Pt2+ cations. Thus the molar ratio between the Pt2+ cations and the number of sorption sites was 1.55. The obtainedplatinum distribution was examined visually and was satisfactory.

Comparative example B

ZSM-5/silica extrudate (30%/70% w/w, calcined at 800° C.) was treatedwith 0.01 M AHS, washed, dried and calcined. The extrudate contained0.048 H+ mmoles/gram extrudate. Hereafter 29.15 gram of the extrudatewas impregnated with about 0.7% platinum by pore volume impregnation in5 minutes with 20.96 ml of an aqueous solution containing 3.59 gram of atetramine platinum hydroxide (Pt(NH₃)₄(OH)₂)-solution (5.9% w/w Pt). ThepH of the solution was >8. The extrudate was not washed but dried by anaccelerated drying profile; by raising the temperature with 15°C./minute to 180° C.; maintaining this temperature for 10 minutes;raising the temperature again with 30° C./minute to 290° C.; maintainingthis temperature for 15 minutes. Hereafter the extrudate was cooled downto room temperature. The molar ratio between the Pt 2+ cations and thenumber of sorption sites was 1.55. No distribution of the platinum wasobtained since the tetramine platinum hydroxide complex did notdecompose.

EXAMPLE 1

ZSM-5/silica extrudate (30%/70% w/w, calcined at 800° C.) was treatedwith 0.01 M AHS, washed, dried and calcined. The extrudate contained0.048 H+ mmoles/gram extrudate. Hereafter 29.15 gram of the extrudatewas impregnated with about 0.7% w/w platinum by pore volume impregnationin 5 minutes with 20.96 ml of an aqueous solution containing 6.82 gramof a tetramine platinum nitrate (Pt(NH₃)₄(NO₃)₂-solution (2.99% w/w Pt)The pH of the solution was about 6. The extrudate was not washed butdried and calcined by an accelerated drying profile; by raising thetemperature with 15° C./minute to 180° C.; maintaining this temperaturefor 10 minutes; raising the temperature again with 30° C./minute to 290°C.; maintaining this temperature for 15 minutes. Hereafter the extrudatewas cooled down to room temperature. The molar ratio between the Pt 2+cations and the number of sorption sites was 1.49. A good platinumdistribution was obtained.

EXAMPLE 2

ZSM-5/silica extrudate (30%/70% w/w, calcined at 800° C.) was treatedwith an AHS solution, washed, dried and calcined. The extrudatecontained 0.048 H+ mmoles/gram extrudate. Hereafter 47.96 gram of theextrudate was impregnated with about 0.7% w/w Nickel by pore volumeimpregnation in about 15 minutes with 30.74 ml of a aqueous solutioncontaining 1.68 gram of a nickel nitrate salt (Ni(NO₃)₂.6H₂O). The pH ofthe solution was about 4. The extrudate was washed and dried andcalcined by an accelerated drying profile; by raising the temperaturewith 15° C./minute to 180° C.; maintaining this temperature for 10minutes; raising the temperature again with 30° C./minute to 300° C.;maintaining this temperature for 15 minutes. Hereafter the extrudate wascooled down to room temperature. The molar ratio between the Ni 2+cations and the number of sorption sites present in the extrudate was5.0. A good nickel distribution was obtained.

A summary of the results obtained in the examples is given in Table 1.In Comparative example A, a satisfactory distribution result wasobtained by using tetramine platinum hydroxide and a slow dryingprofile. When an accelerated drying profile was used instead of the slowdrying profile, as illustrated in Comparative example B, the tetramineplatinum hydroxide complex was found not to decompose. When thiscatalyst was subsequently activated in a reductive atmosphere, amigration of Pt to the exterior of the catalyst was observed, resultingin an unacceptable loss of performance. Examples 1 and 2 show that anaccelerated drying profile can be used, while obtaining at the same timefull decomposition of the complex as well as a good distribution, when aGroup VIII metal nitrate complex is used according to the invention.

TABLE 1 pH of ratio of Group Ex- Group VIII the Form of the VIII metalperi- metal salt solu- molecular drying cations over Distribution mentused tion sieve profile sorption Sites result A Pt(NH₃)₄(OH)₂ >8 H-formslow 1.55 satisfactory B Pt(NH₃)₄(OH)₂ >8 H-form accelerated 1.55 thecomplex did not decompose 1 Pt(NH₃)₄(NO₃)₂ ±6 H-form accelerated 1.49good 2 Ni(NO₃)₂.6H₂O ±4 H-form accelerated 5.0 good

We claim:
 1. A method comprising: a) contacting a molecular sieve-binderextrudate having sorption sites, with an aqueous solution of acorresponding Group VIII metal nitrate salt having a pH of below 8 andin the essential absence of ammonium ions, wherein the molar ratiobetween the Group VIII metal cations in the solution and the number ofsorption sites present in the extrudate is equal to or larger than 1,wherein the binder comprises a silica binder material, wherein thenumber of sorption sites in the molecular sieve-binder extrudate isreduced prior to the impregnation of the Group VIII metal by means of adealumination treatment which treatment comprises contacting themolecular sieve-binder extrudate with a solution of ammoniumhexafluorosilicate; and wherein the molecular sieve is in its H-form;and, b) drying the molecular sieve-binder extrudate obtained from stepa) in accordance with an accelerated drying profile by which thetemperature of the molecular sieve-binder extrudate obtained from stepa) is raised to no more than 300° C. and for a duration of less than 90minutes prior to the use of the resulting dried, impregnated molecularsieve-binder extrudate.
 2. The method of claim 1 wherein the molar ratiobetween the Group VIII metal cations and the number of sorption sites isbetween 1 and
 20. 3. The method of claim 1 wherein the Group VIII metalis Ni, Pt, and/or Pd.
 4. The method of claim 1 wherein the Group VIIImetal nitrate salt is Ni(NO₃)₂, Pt(NH₃)₄(NO₃)₂ or Pd(NH₃)₄(NO₃)₂.
 5. Themethod of claim 1 wherein the molecular sieve is of the MFI, TON, MTT orMTW type.
 6. The method of claim 1 wherein step a) is performed with anaqueous solution of the corresponding Group VIII metal nitrate salthaving a pH in the range from 3.5 to
 7. 7. The method of claim 1 whereinstep a) is performed by pore volume impregnation.
 8. The method of claim1 wherein the molecular sieve is in its H-form before impregnation.
 9. Amethod of claim 1, wherein the accelerated drying profile comprises thesteps of: raising the temperature of the molecular sieve-binderextrudate obtained from step a) at a rate in the range of from 10° C. to20° C. per minute to a first temperature in the range of from 150° C. to200° C.; maintaining the first temperature for a time period in therange of from 5 to 15 minutes; thereafter raising the temperature at arate in the range of from 10° C. to 40° C. per minute to a secondtemperature in the range of from 250° C. to 300° C.; maintaining thesecond temperature for a time period in the range of from 10 to 20minutes; and thereafter reducing the temperature.